Pressure compensated ionization chamber fire detector system



Feb. 19, 1963 R. E. BRESSLER 3,078,450

PRESSURE COMPENSATED IONIZATION CHAMBER FIRE DETECTOR SYSTEM Filed Aug.3, 1961 4 Sheets-Sheet 1 FIG. 1.

\ INVENTOR ROBERT EJEsREsSLEYL IBYMVW ATTORNEYS Feb. 19, 1963 R. E.BRESSLER 3,078,450

PRESSURE COMPENSATED IONIZATION CHAMBER FIRE- DETECTOR SYSTEM Filed Aug.3, 1961 V 4 Sheets-Sheet 2 W10 ACTIVE, MATERIAL 157 Q H H3 9/: QE 5% a gg g ///1 EL\\\\\\+// //////L\Y/l/l/ l INVENTOR 3 2 i3 ROBERT E. BRESSLBRM 9- W A ORNEYJ 1963 R. E.BRESSLER 3,078,450

PRESSURE CQMPENSATED IONIZATION CHAMBER FIRE DETECTOR SYSTEM Filed Aug.3, 1961 4 Sheets-Sheet 3 10 1g n E3 13/9 q g)? Q RADIO ACTIVE MATER n\ N3 i ,fi or a d Q\ I V i I IfIVENTOR B "0 3 3. Q 2% g t 3 Q ROBERT EBRESSLER Mfi W ATTO EYS 1963 R E. BRESSLER 3,078,450

PRESSURE COMEENSATED IONIZATION CHAMBER FIRE DETECTOR SYSTEM 4Sheets-Sheet 4 Filed Aug. 3, 1961 FIG. 5'.

To ALARM C lRCUlT INVENTOR ROBERT E.BRESSLER BY v ATTORNEYS UnitedStates Patent 3,7S,45li PRESSURE COMPENSATED EUNIZA'EHQN CHAM- BER FllREDETETUR SYEiTEM Robert E. Eressler, Oregon, Ell, assignor to Martin J.McGinn, (Pregon, ill. Filed Aug. 3, N61, Ser. No. 129,137 1? Qlaims.(Cl. fi th-23?) This invention relates to apparatus responsive tochanges In the composition of a gas, and more particularly to anionization type detection type device for testing air for the presenceof smoke and other combustion products.

This application is a continuation-in-part of my patent applicationSerial Number 46,601, filed July 28, 1960, now abandoned.

ionization type detectors for the presence of smoke and combustionproducts have the advantage that they dotect the presence of combustionduring its earliest stages or during What is known as the incipientperiod when combustion gases alone are being produced by the combustion.On the other hand, fire detection devices of the thermostatic orphotoelectric type only respond to the later stages of the combustionwhen the fire has become well established. it is obvious, therefore,that a fire or combustion detection device which operates upon theionization principle is much more effective in providing an earlyWarning of the presence of combustion than detection devices of othertypes.

Ionization type combustion detection devices are known per se and areshown, for example, by United States Patent Number 2,465,377, issued toWalter C. Iaeger, on Inarch 29, 1949, and United States Patent Number2,702,898, issued to Ernst Meili, on February 22, 1955.

Combustion gas detection devices of the type shown by the Jaeger andMeili patents include a test ionization chamber which is open to theatmosphere in which the combustion gases are being detected, andcontaining therein a small quantity of a radioactive material, such asradium, which emits alpha particles to render the air in the ionizationchamber conductive by ionizing air molecules in the chamber. The testionization chamber is connected electrically in series with a referencechamber which alsocontains radioactive material similar to thatcontained in the test chambers. The reference chamber should beconstructed in such manner as to prevent the entrance therein of thecombustion products or smoke particles. The reference chamber is ineifect a resistance element electrically connected in series with thetest chamber.

in the presence of visible or invisible smoke particles in theatmosphere being monitored, the smoke particles entering the open testionization chamber impede the passage of the alpha radiation emitted bythe radioactive source in the test chamber, and reduce the number ofelectrons and ions formed from the air molecules in the chamber by theionization action of the radiation source. This results in a decrease ofionization current in the presence of combustion gases caused by theincipient fire. Since the ionization chamber is connected electricallyin series with the reference chamber across a direct current voltagesource, a change in ionization current in the test chamber causes aredistribution of the voltages across the reference chamber and theionization chamber, which always must equal the total applied voltage.Thus, if the control electrode of a gaseous discharge tube is connectedat the electrical junction between the test chamber and the referencechamber, the change in potential at the point of connection of thecontrol electrode due to the redistribution of voltages across the testand reference chambers in the presence of combustion prodnote can beused to trigger the firing of the tube. The firing of the control gastube may be used to actuate a ice suitable signaling device whichindicates the presence of the combustion gases and the incipient fire.

In the operation of ionization detection devices for detecting presenceof combustion gases, it has been noted that the conductivity of theionization chambers are influenced to an important degree by densitychanges in the gases present therein. Normal atmospheric pressure andtemperature fluctuations change the density of the atmospheric airsensed by the test chamber so that unless compensated for, thecombustion gas detecting device must be adjusted for low sensitivitywith respect to smoke to insure against false operation due totemperaure or barometric variations. This problem becomes paricularlyacute where the detection device is used on aircraft or under otherconditions of extreme density variations. Thus, in the device of theJaeger Patent 2,465,377, since the interior of the reference chamber ishermetically sealed while the test chamber is open to atmosphericpressure, variations in atmospheric pressure iniluence only the testchamber and do not similarly influence the reference chamber, with theresult that with the device of laeger, barometric pressure changes cancause a false indication of the detection device.

in the installation and operation of ionization type combustiondetection devices, it is frequently necessary and desirable to makeadjustments for manufacturing variations in the triggering voltage ofthe control tube used in conjunction with the device, and also to adjustthe sensitivity of the detection device.

Another problem which arises in connection with the operation ofionization type combustion detection devices is that a number of suchdevices are frequently installed at spaced locations and have theiroutputs electrically connected in parallel so as to actuate only asingle alarm device, with the result that it is sometimes difiicult toidentify the particular detector device which detected the combustion.products.

Accordingly, it is an object of this invention to provide a combustiongas detection device of the ionization type which is not sensitive tochanges in the density of the atmosphere being monitored.

It is another object of the invention to provide a combastion gasdetection device of the ionization type which is compensated for changesin atmospheric pressure while still remaining hermetically sealed.

It is still another object of this invention to provide a combustion gasdetection device of the ionization type including a reference chamberand a. test or sensing chamher in which the reference chamber iscompensated for changes in the atmospheric pressure while, at the sametime, maintaining the reference chamber hermetically sealed.

it is a further object of the invention to provide in combination withan ionization type combustion detector, a convenient and accurate meansfor permitting adjustment of the sensitivity of the detection device andpermitting compensation for manufacturing variations in the triggeringvoltage of the control tube.

Still a further object of the invention is to provide in combinationwith an ionization type combustion detection device, an indicating lightwhich is part of the detection device assembly to give a visualindication directly at the location of the indicating de ice of thedetection of combustion products.

Still a further object of the invention is to provide an ionization typecombustion detector including a hermetically sealed and totally enclosedreference chamber which is compensated for changes in atmosphericpressure, and in which the electronic control tube of the combustiondetection device is housed within the hermetically sealed referencechamber to thereby eliminate the possibility of condensate deposit onthe tube due to temperature changes which would adversely affect theoperating characteristics of the tube and of the combustion detectiondevice.

Still a further object of the invention is to provide adjustment meansfor equalizing the internal pressure of the reference chamber with thatof the atmosphere at any time, and to permit equalizing the referencechamber pressure with the atmospheric pressure of various localities inwhich the fire detection device may be installed.

In achievement of these objectives, there is provided in accordance withthis invention, a combustion gas detection device of the ionization typeincluding a test chamber having radioactive material therein and open tothe atmosphere, and a reference chamber electrically connected in serieswith the test chamber across a source of electrical potential, thereference chamber also containing a source of radioactive materialtherein. In accordance with an important feature of the construction,the reference chamber is hermetically sealed, but includes a means suchas a flexible diaphragm or bellows for communicating variations in theexternal atmospheric pressure to the interior of the reference chamber,whereby the gas pressure inside the reference chamber is alwayscompensated for changes in the external atmospheric pressure, or of thegaseous medium in which the detection device is immersed, and equalizedwith the gas pressure in the test chamber.

In further achievement of these objectives, there is provided inaccordance with one embodiment of the invention, the combination with anionization type combustion detector of an adjustable shielding means forthe radioactive material in the test chamber to permit controlling thestrength of the radiation of the test chamber. This, in turn, can beused to adjust the operating potential on the control electrode of thegaseous discharge control tube and to adjust the sensivity of thedetection device. In another embodiment of the invention, there isprovided the combination of an ionization type detector with a fixedsource of radioactive material in the test chamber, together with theconnection of the outer electrode of the test chamber to the adjustabletap of a potentiometer to permit adjustment of the total voltage acrossthe test and reference chambers. By connecting the cathode of thegaseous discharge control tube to an end of the potentiometer,adjustment of the potentiometer tap connection to the test chamberelectrode can be used to adjust the operating potential on the controlelectrode of the gaseous discharge tube to compensate for manufacturingvariations in the triggering voltage of the control tube, or to adjustthe sensitivity of the detection device.

In accordance with another feature of the invention, there is providedas part of the combustion detection device assembly, an indicating lampwhich is connected between the anode and cathode of the gaseousdischarge control tube in series with a normally open contact which ismoved to closed position upon energization of a relay connected inseries with the cathode of the control tube, to thereby energize theindicating light. Alternatively, the indicating lamp may be connected inparallel with a resistance in the anode circuit of the gaseous dischargecon trol tube.

In accordance with a further embodiment of the invention, the gaseousdischarge electronic control tube used with the combustion detectiondevice is housed within the hermetically sealed reference chamber,thereby preventing the deposit of condensate on the control tube whichwould adversely affect the operation of the control tube and of thecombustion detection device.

A still further feature of a modified embodiment is the provision of ascrew valve member which may be opened when the combustion detectiondevice is initially installed in any given location to equalize thepressure between the interior and exterior of the bellows, after whichthe screw valve is closed. This initial adjustment permits the internalpressure of the bellows to be conformed to the mean pressure at anylocality where the fire detection device may be installed.

Further objects and advantages of the invention will become apparentfrom the following description taken in conjunction with theaccompanying drawings in which:

FIGURE 1 is view of a combustion gas detection device in accordance withthe invention;

FIGURE 2 is a schematic wiring diagram of the electrical circuitconnections of the device shown in FIG. 1;

FIGURE 3 is a view in elevation, and partially in section, of a modifiedcombustion gas detection device in accordance with the invention,including a schematic diagram of the electrical circuit connections;

FIGURE 4 is a view in elevation, and partially in section, of anothermodified combustion detection device in accordance with the invention,including a schematic diagram of the modified electrical connectionstherfor;

FIGURE 5 is a view in vertical section, and partially in elevation, of amodified hermetically sealed fire detection device in which theelectronic control tube is housed within the hermetically sealedreference chamber;

FIGURE 6 is a perspective view of the device of FIG. 5; and

FIGURE 7 is a wiring diagram of the modified corn bustion detectiondevice of FIGS. 5 and 6.

Referring now to the drawings, and more particularly to FIGS. 1 and 2,there is shown a combustion gas detector device generally indicated atit), including a test chamber 12 which is immersed in the gas beingmonitored for the presence of combustion products, such as the atemosphere of a room. Test chamber 12 is bounded by a perforated metallicwall 14 made of metallic wire mesh or otherwise suitably perforated toadmit the ambient atmosphere. Perforated wall 14 is mechanically andelectrically connected at its upper end to a generally cylindrical metalwall 16 which, in turn, is suitably supported by a mounting base throughwhich extend electrical conmotions for the various elements of thedevice, as will be described hereinafter. The perforated wall 14 issuitably connected through wall 16 and conductor 58 to the negative sideof the direct current power source and forms the outer electrode of testchamber 12. A source of radioactive material indicated at 22, such asradium, is suitably supported upon the inner surface of wall 14 by aholder generally indicated at 23, having an adjustable shielding cap 25and shown and described more fully in connection with the embodiment ofFIG. 3.

The inner electrode 20 of test chamber 12 is positioned in chamber 12 inspaced relation to perforated wall 14. Inner electrode 20 is suitablysupported by the wall of a hollow envelope generally indicated at 24,made of a th electric material such as glass. Envelope 24 is dividedinto two separate compartments which respectively house a reference orcomparison chamber 26 and a cold cathode gas discharge tube 28.

The reference or comparison chamber 26 has positioned on the inner wallsurface thereof a conductive coating which defines an electrode 39, anda radioactive material 32 is positioned on a portion of the surface ofelectrode 3t). Electrode 3d and radioactive material 32 are electricallyconnected by conductor 34 to electrode 29 positioned in test chamber 12.

A second or inner electrode 36 is positioned in reference chamber 26 inspaced relation to the walls thereof and in spaced relation to electrode36 defined by the conductive coating. Inner electrode 36 is connected byconductor 51 to the positive side of the source of direct currentelectrical potential, as will be seen by reference to the wiring diagramof PEG, 2.

In accordance with an important feature of the inven tion, a bellowsgenerally indicated at 38 is positioned on the outside of envelope 24adjacent reference chamber 26 and communicates variations in thepressure of the gas being monitored to the interior of reference chamber26, so that the gas pressure interiorly of reference charm ber 26 variesin the same manner as, and is equalized with, the gas pressure in testchamber 1?... The volume of the bellows should be proportional to thesize of the reference chamber 26 as related to the pressure of theenvironment in which the detection device will be used, so that thebellows can continuously equalize the pressure interiorly of referencechamber 26 with the pressure in test chamber 12.

Mounted in the same insulating envelope 24 as refercnce chamber 26, butseparated from chamber 25 by a barrier wall 4% is cold cathode gaseousdischarge tube 2% having positioned therein an anode 42, a cathode 44,and a control grid -16.

Control grid 46 of gaseous discharge tube 28 is connected by conductor24 to the inner electrode 311 defined by the conductive surface insidereference chamber 26 and to the coating of radioactive material 32carried by electrode 31 Control grid 45 is also connects to innerelectrode 21 of test chamber 12. Thus, electrode 219 of test chamber 12and electrode 3% and radioactive material 32 of reference chamber 26,and control grid as of gaseous discharge tube 28 are all at a commonelectrical potential. In order to prevent any external electricalinfluences from affecting the potential of grid id, envelope 24 isheavily insulated in the region of barrier wall it of the envelope asindicated at 45.

Cathode 44 of gas tube 28 is connected to the negative side of the powersource by conductor 43 and is at the same potential as the perforatedscreen outer electrode 14 of test chamber 12. Anode 42 of gaseousdischarge tube 28 is connected to the positive side of the DC. powersource by conductor 4%. A condenser 55 is connected between grid as andcathode d4 of gas tube 8.

A relay coil 56 is interposed in series with the output of anode 4-2 ofgas tube 2% and when energized, operates to closed position, a noruiallyopen contact 58 in a suitable alarm or signaling circuit which, whenenergized, indicates that combustion products are present in the gaseousatmosphere being monitored by test chamber 12.

in the operation of the device, assuming that there are no combustionproducts present in the atmosphere being monitored, :1 current will flowthrough the series circuit comprising test chamber 12 and referencechamber 26, due to the potential applied between the pair of electrodes14-21) and Cid-36 or" each of the respective chamber-s 12 and 26 and dueto the presence of the radioactive material 22 or 32 in each of therespective chambers 12 and 25 which causes ionization of the air in therespective chambers and, in combination with the potentials applied tothe electrodes of the respective chambers, causes a current to flowthrough each of the series-com nected chambers.

When there are no combustion products present in the gas being monitoredby test chamber 12, the voltage drops across the respective chambers 12and 26 are such that the potential of junction point 45 to which triggergrid as of gaseous discharge tube '28 is connected, is such that thepotential of grid 46 is not sufiiciently positive with respect tocathode 44 to cause discharge and consequent ionization of gas in tube2%. However, in the presence of combustion products in the gas monitoredby test chamber 12, the combustion gases in test chamber 12 present animpedance to the flow of current in test chamber 12 which causes thepotential of grid or trigger 46 to become relatively more positive withrespect to cathode 44, to thereby trigger the firing of tube 23, causinga current flow through relay coil 56 in the circuit of anode 42, which,in turn, closes contact 58 in the alarm circuit. When the potential ofgrid or trigger 46 becomes sufficiently positive to tire tube 2%,condenser 55 discharges between grid 45 and cathode 44 and aids instriking an are between cathode 44 and anode 42.

Due to the use of bellows 38, the gas pressure inside reference chamber'26 is always equalized with the pressure of the gas environment inwhich test chamber 12 is immersed, thereby avoiding any erroneoussignals due to a mere change of barometric pressure of the surroundingatmosphere, and permitting the fire detection device to be adjusted forhigh sensitivity to smoke or other combustion products.

Another embodiment of the invention is shown in the drawing of FIGURE 3,which shows a combustion gas detection devi e generally indicated at1110 including a test chamber 1M open to the atmosphere and a referencechamber 1114 which is sealed from the atmosphere, but which is subjectedto atmosphereic pressure due to the use of a flexible diaphragm 106which closes one end of reference chamber 1114-.

The combustion gas detection device 1111 in the embodiment of FIG. 3includes a plurality of cylindrical sections or rings 1118, 110, 112,and 114 each of the same inner and outer diameter and stacked insuperposed relation to each other to define a hollow cylindrical body.Rings 108, 119, 112, 114 are all made of a non-hygroscopic insulatingmaterial having a high dielectric constant, and may be made of hardrubber, for example. Axially spaced from and below the bottommost ring1% is a metal disc electrode member 116 having the same diameter as theouter diameter of the insulating rings and axially spaced from thebottom surface of ring 1138 by insulating bushings or sleeves 118, threeof which may be positioned at equally circumferentially spaced pointsabout the periphery of the device 1%. Disc electrode 116 forms thebottom wall of open test chamber 1112.

Insulating bolt member 121) extend through axial passages in sleeves 118and rings 1%, 111), 112, and 114, and also through an upper disc-shapedclosure 122 which is clamped against the upper end of topmost ring 114,with respect to the view shown in FIG. 3, by nut members on the ends ofbolts 120. Closure 122 has an aperture 142 therein which admitsatmospheric pressure to the upper surface of diaphragm 1%.

A holder 124 for radium or other radioactive material is rigidly fixedto the disc electrode 116, support 124 projecting upwardly into theinterior of test chamber 162. Support 124 includes a post member 126having a reduced neck portion at the upper end thereof about which ispositioned the radioactive material 128. In order to control the amountof radiation of the radioactive material 123, an adjustable cap member131] is secured to and turns with the upper end of a screw member 132,the lower end of screw 13-2 being received within the hollow interior ofpost 126 and the threaded portion of screw 132 passing through athreaded passage in the upper portion of post 126. By adjusting screw132 against the pressure of a spring 134- positioned Within the hollowinterior of post 126, the position of shielding cap 131) relativeto theradioactive material 123 may be adjusted to control the degree ofradiation from material 128.

A metal disc 136 is received betwen the surfaces of insulating rings 1&8and 11d and defines a common electrode for both the test chamber 162 andreference chamber 1114. Radioactive material 137 is positioned onelectrode 136 in reference chamber 104.

A second electrode in reference chamber 194 is provided by a metal disc138 secured between the adjacent surfaces of rings 11% and 112. The disc138 has an opening 1% therein so that there is free gaseouscommunication between the portion of reference chamber lying betweenelectrodes 136 and 138 and the portion of chamber 1% lying betweenelectrode 138 and flexible diaphragm 1%.

The top wall of reference chamber 104 is formed by the flexiblediaphargm 1116 having its outer periphery secured between the adjacentsurfaces of insulating rings 112 and 114. The flexible diaphragm 106 maybe made of any suitable material such as plastic or leather which hasthe necessary flexibility to respond to changes in pressure of theatmosphere in which thedevice 1111) is positioned, so as to constantlyequalize the pressure between reference chamber 104 and the atmospheresurrounding the combustion detection device 1%. Equalization of the gaspressures as just described of course results in constantly equal gasdensities in the reference chamber 164 and test chamber 1412, therebypreventing any false actuation of gas tube 151 due merely to adifferential be tween the density of the gas in the reference chamber164 and the gas in test chamber 102. Furthermore, the flexible diaphragm1156 maintains reference chamber 1114 hermetically sealed, preventingthe entrance of moisture and foreign matter which would adversely affectthe operation of the device, and yet permits constant equalization ofthe pressure and density of the gas in reference chamber 164 to that ofthe surrounding atmosphere.

Metal disc 122 forms the top wall of the device ran and is provided withan opening 142 which permits a free communication of the gaseousatmosphere outside the device 1116* into the space above the flexiblediaphragm 1116.

The disc electrode 116 of open test chamber 162 is connected to thenegative side of the direct current source of power by conductors 121,125, while the disc elcctrode 138 of reference chamber 1114 is connectedto the positive side of the direct current source of power by conductors125, 127. Thus, the test chamber 132 and the reference chamber 11W areconnected in series across the direct current power source, with theconductive path between electrode 116 of test chamber 1G2 and the commonelectrode 136 being provided by the ionized particles due to theradiation from source 128 in test chamber 192, while the conductive pathin reference chamber 1114 between common electrode 136 and electrode 158is provided by the ionized particles due to the radiation from radiationsource 137 in chamber 104.

Immediately adjacent the test and reference chambers is a cold cathodegaseous discharge tube 150 including a cathode 152, an anode 154, and acontrol grid or trigger 156. Cathode 152 is connected to the negativeside of electrical power in parallel with electrode 116 of test chamber1112, while control grid or trigger 156 is connected to the commonelectrode 136 of test chamber 102 and reference chamber 1114. Acondenser 155 is connected between grid 156 and cathode 152 and helps toinitiate the arc discharge across tube 15d when the potential of grid ortrigger 156 becomes sufliciently positive to fire the tube. Anode 154 ofgas tube 159 is connected to the positive side of power by conductor 127in series with a relay coil 158 which, when energized, operates acontact 160 to closed position to energize a suitable alarm device 162.

In order to provide directly at the location of the detection device11kt) a visual indication of the firing of tube 150 and consequently ofthe presence of combustion products, an indicating light 164 isconnected across anode 154 and cathode 152 in series with a normallyopen contact 168 which is operated to closed position upon theenergization of a relay coil 166 connected in series with cathode 152 oftube 150. When tube 1511 is not conducting, relay coil 166 remainsunenergized, and contact 168 remains open. Consequently, indicatinglight 164 remains unlighted. However, if gas tube 151 becomes conductingdue to the presence of combustion products, relay coil 166 is energizedto close contact 168, thereby energizing indicating light 164 to providea visual indication of the presence of combustion gases. Since aplurality of detection devices 1% may be connected to only a singlealarm device 162, operation of the alarm device 162 would notnecessarily indicate which one of the plurality of detection devices 1%had detected the presence of combustion products. However, by pro--viding an indicating lamp 164 as part of the assembly of each detectiondevice 1110, the energization of any indicating lamp 164 will indicatewhen its associated detection device has detected the presence products.

The operation of the detection device 1th) is substantially the same asthat previously described for the detection device of the embodiment ofFiGS. 1 and 2 and will not be described again in detail. When combustionproducts are not present in the vicinity of the device 1111}, thedistribution of voltages across the seriesconnected test and referencechambers 1112 and 104 is such that the potential of control grid ortrigger 156 connected to common electrode 136 is not sufiicientlypositive to permit firing of gaseous tube 1511. However, in the presenceof combustion products in test chamber 1112, the impedance to flow ofionization current in chamber 1112 increases to cause a redistributionof voltages across the chambers 1G2 and 1% such that the potential ofcontrol grid or trigger 156 becomes sufliciently positive to trigger thefiring of gaseous discharge tube 15% Conduction of tube causesenergization of relay coil 15% in the anode circuit of the tube tothereby close contact 1611 and energize alarm device 1162. Conductionthrough tube 156 also energizes relay coil 166 to close contact 168 andenergize indicating light 164.

There is shown in FIG. 4 a modified embodiment including a combustiongas detection device generally indicated at 101) which is generallysimilar to the detection device shown in FIG. 3, with parts of thedevice 1% which are similar to the device 1% of FIG. 3 being indicatedby primed reference numerals corresponding to those of FIG. 3. Thedevice 1% will not be described in detail except to point out that itincludes a test chamber 102', a reference chamber 164', a disk electrode116' forming the bottom of text chamber 1112', a common electrode 156'for the test chamber 102' and reference chamber 164', and an electrode138' for the reference chamber 164. A non-adjustable source ofradioactive material such as radium indicated at 2011 is positioned on ametal support 2132 extending upwardly from the inner surface of the diskelectrode 116 of test chamber 192'. A cold cathode gaseous dischargetube generally indicated at 1511' forms part of the detection deviceassembly and includes an anode 154, a cathode 152' and a controlelectrode 156'.

In accordance with an important feature of the em bodiment of FIG. 4, apotentiometer 2 94 has one of its ends 2116 connected to the positiveside of the direct current power source, while its opposite end 208 isconnected to the negative side of the direct current power source. Diskelectrode 116 of test chamber 102 is directly connected to a movable tap21d on potentiometer 2114, while electrode 138' of reference chamber104' is connected directly to the positive side of power by con ductor212 and is thus at the same potential as the end 2116 of potentiometer2414. It will be seen that the total voltage across the twoseries-connected chambers 1G2 and 104 can be adjusted by moving theposition of tap 2111 along the potentiometer 2114 Control electrode 156of combustion of gaseous discharge tube 150' is directly connected tothe common electrode 136' of the chambers 102' and 104'.

It will be noted in the embodiment of FIG. 4 that the potential betweencontrol electrode 156 and cathode 152', unlike the embodiment of FIG. 3,is not always equal to the potential drop across test chamber 162',since the voltage difference between control electrode 156 and cathode152 is equal to the sum of the voltage drops across chamber 1112' fromelectrode 136' to electrode 116', which is connected to tap 2113 ofpotentiometer 204, plus any voltage drop which may exist acrosspotentiometer 2&4 between tap 21d and end 2% of the poteniometer,depending upon the position of tap 2111. By adjusting the position oftap 2 1 1, the potential of control electrode 156' with reference tocathode 152' can be adjusted to provide the proper operating voltagelevel at the control electrode 156' to compensate for any manufacturingvariations in the triggering voltage of the tube 150 and also to adjustthe sensitivity of the detection device. Thus any necessary adjustmentof the voltage level on the control electrode 155' or of the sensitivityof the detection device can be made by adjusting the posiiton of tap 210on potentiometer 204, permitting the use of a non-adjustable source ofradioactive material 2% in test chamber 192.

In the embodiment of FIG. 4, relay coil 158' is connected in series withanode 1:34 to close contact 160 to energize alarm device I162 when thecontrol tube 1550" becomes conductive, as in the embodiment of FIG. 3.

Also, an indicating lamp 164 is directly connected between anode 154 andcathode 152 in series with a normally open contact 68. Relay coil 166 isconnected in series with cathode 152' and is energized when tube 15%)becomes conductive to close contact 16%", thereby completing the circuitof indicating lamp 164'. Since indicating lamp 164 is directly connectedbetween anode 154- and cathode 152', the voltage which energizes lamp164 is the voltage drop which exists across tube 150 after breakdown hasoccurred.

There is shown in F165. 5, 6 and 7 a modified fire detection devicegenerally indicated at 3%, including an outer metal shell or casinggenerally indicated at 302 having a downwardly tapered wall 364terminating at its lower end in a normally horizontal base 3%. Asparticularly shown in FIG. 6, the base 306 is cut away to leave acircular flange 3G8 at the outer periphery of the base, a central hubportion Silt), and a plurality of radiating spoke portions 312connecting hub 31a and outer flange 3%. The surface area of base 365 notoccupied by flange 3tl8, hub 31%, or radial spokes 312 defines openings314 which permit passage therethrough of the air or gas which is beingmonitored for the presence of the combustion products. The tapered wall3634 is also provided adjacent the lower end thereof with a plurality ofcircumferentially spaced openings 31.6. The air or gas which is beingmonitored circulates through the openings 314 in base see and throughthe openings 316 in the lower portion of tapered wall 3G4. The outermetal casing 3&2, including its tapered wall 3%- and its base portion 3%comprises one of the electrodes of the combustion detection device aswill be described more fully hereinafter in the explanation of theelectrical circuit of the device.

A holder 324 for radium or other radioactive material is rigidly fixedto the hub portion 310' of base 3%. Support 324 is generally similar tothe holder 124 described in connection with the embodiment of FIG. 3 andincludes a post member 326 having a reduced neck portion at the upperend thereof about which is positioned the radioactive material 328. Inorder to control the amount of the radiation of the radioactive material323, an adjustable shielding cap 336 is secured to and turn with theupper end of screw member 332. The lower end of screw 332 is receivedwithin the hollow interior of post 32:; and the threaded upper portionof screw 332 is in screw-threaded engagement with a screw-threadedpassage in the upper portion of post 326. By adjusting screw 332 againstthe pressure of spring 334 positioned within the hollow interior of postass, the position of shielding cap 3 3i} relative to the radioactivematerial 328 may be adjusted to control the degree of radiation from theradioactive material.

The space bounded by the base see of metal casing 392, by the lower endportion of the inner surface of tapered wall 334 of casing 3% adjacentopenings 316, and by the lower surface of base portion 364 of commonelectrode 362, to be described, constitutes the test chamber 335 of thecombustion detection device.

Positioned within the outer metal casing 3% and coaxially thereof, is aninner insulating housing generally indicated at 33-5 of a suitableplastic or other insulating material, which houses the reference chamberand the gaseous discharge control tube, as will be explained more fullyhereinafter. Inner housing 336 is of hollow interior and includes anupper portion 338 of larger internal diameter and a lower portion 340 ofsmaller internal diameter. An annular horizontal flange 342 extendsradially outwardly from the upper end of inner housing 336. Achannel-shaped annular flange 34-4 extends downwardly from adjacent theouter peripheral edge of hori zontal flange 342 of housing 336, annularchannel-shaped flange 344 having a circumferential groove 346 thereinwhich receives the upper peripheral edge of outer metal casing 304.Screws or other suitable fastening means 348 extend through apertures inchannel-shaped flange 344- and through the upper edge of metal casing304 in order to secure metal casing 3% to the inner insulating housing336. An annular flange 35% extends vertically upwardly from the outerperipheral edge of horizontal flange 342 and is received in an annulargroove 354 in an insulating base member generally indicated at 352 whichis secured to the ceiling or other supporting surface on which thecombustion detection device 300 is mounted. The insulating base 352 alsoincludes a plurality of plug-in receptacles 356 which receivebayonet-type contact plug members 35S carried by housing 336 of thecombustion detection device 3% to elfect the various electricalconnections shown in the wiring diagram of FIG. 7.

An annular flange 3&9 extends radially inwardly from the inner surfaceof lower portion 340 of insulating housing 536, and a metal electrodemember generally indicated at 362 has its disk-shaped base 364 seatedagainst and hermetically sealed to the under surface of flange 36%.

Integral with the disk-shaped base 364 of electrode 362 is an upstandinghollow cylindrical electrode portion 366 which extends verticallyupwardly from the upper surface of base portion 364 of electrode 362.Base portion 364 of electrode 362 bounds the lower end of the referencechamber generally designated 368, the upper end of the reference chamberbeing bounded by the top end of the bellows 4% to be describedhereinafter. Radioactive material, indicated at 369, similar to theradioactive material 328 of the test chamber, is positioned on theradially outer surface of cylindrical electrode portion 366.

Positioned coaxially outwardly of cylindrical electrode portion 365 anddefining a second electrode in the reference chamber 368 is acylindrical electrode 370 which is preferably formed of wire mesh screenmetallic material. Outer cylindrical electrode 376 is radially spacedoutwardly from cylindrical electrode portion 366 of electrode 362, toprovide an annular space between the two electrodes 370 and 362. Fixedto the upper end of electrode 373 is a radially outwardly extendingannular flange 372 which rests on and is suitably secured to a shoulder374 in the inner wall of insulating housing 336 adjacent the junctionbetween large diameter portion 333 and small diameter portion 3% ofinsulating housing 335.

The use of the wire mesh metallic screen material for outer cylindricalelectrode 37d has the advantage over a solid surface electrode that thelength of the travel path of the alpha particles is extended, since thealpha particles pass through the screen of which electrode 375% isformed, but return to the screen due to the electrical potentialthereon. The longer travel path thus provided for the alpha particlesincreases the ionization in the reference chamber and insures that thereference chamber operates in its saturated range.

A cold cathode gaseous discharge control tube 330 is positionedvertically within the upstanding hollow cylindrical electrode portion366 of electrode 362. The location of tube 389 within the hollowinterior of electrode portion see serves to shield the tube from theradioactive material 369 positioned on the outer surface of hollowelectrode portion 366, this shielding being particularly important inthe region of control grid 382 of tube 33%.

The control tube 380 includes a control grid 332 which extends throughthe lower end of tube 3liwith respect 1 i 1 i to the view shown in FIG.5, grid 332 being electrically connected by soldering or the like tobase portion 364 of common electrode 362. Tube 33% also includes anode384 which, as best seen in the wiring diagram of FIG. 7, is connected byconductor 386 to the outer cylindrical electrode 37% in the referencechamber 368. Control tube 330 also includes a cathode 338 which isdirectly connected to the negative side of the power supply. The outercasing 332, including tapered wall 334 and base 306 of test chamber 335is connected to the negative side of the power supply through a springclip contact 389. The negative side of the power supply is conductedthrough the upper mounting base 352 to the insulating housing 336through the engagement of bayonet contact plug members 358 and plug-inreceptacles 356, and thence is connected to the outer metal casing 302by spring clip contact 389 to thereby cause the casing 302 and its base396 to become an electrode of test chamber 335.

Outer casing 332 instead of being made of electrically conductive metalmay instead be made of plastic or other suitable insulating material. Inthis case, spring clip 339 would be eliminated and post member 326 intest chamber 335 would be directly connected to the negative side of theelectric power supply through a conductor connected to a bayonet plugmember 358 which in turn engages a plug-in receptacle 356 connected tothe negative side of the electric power supply.

As best seen in the wiring diagram of FIG. 7, a condenser 390 isconnected between control grid 382 and cathode 388 to initiate the arcdischarge across gaseous discharge tube 360 when the potential of gridor trigger electrode 382 becomes sui'ficiently positive to fire thetube.

Anode 334 of tube 380 is connected to the positive side of the powersupply in series with a resistance 392 and a relay coil 394. Relay coil394, when energized by current flow through the output circuit of anode384, closes contacts 396 in a suitable alarm circuit.

A signal lamp 395 which is carried by the mounting base 352 is connectedacross resistance 392 in the circuit of anode 384. Thus, when thepotential drop across resistance 392 becomes suflicient due to thefiring of tube 380 and consequent conduction through the output circuitof anode 384, the signal lamp 398 is energized to indicate that thecombustion detection device 380 has been actuated by the presence ofcombustion products. As previously pointed out, a plurality ofcombustion detection devices such as 300 may be connected in parallelwith each other in the circuit of a single alarm device, and the signallamp 393 provided on each of the combustion devices 3% serves toidentify which of the combustion detection devices actuated the alarm.

In order to hermetically seal the reference chamber 363 to preventthe-entrance of moisture and foreign matter therein which wouldadversely affect the operation of the device, and also to hermeticallyseal the gaseous discharge tube 334) to prevent condensation of moistureand other matter thereon which would adversely afiect its operatingcharacteristics, a bellows 400 is positioned within the hollow interiorof the upper portion of insulating housing 336. In addition to thefunctions just mentioned, the bellows 4% of course serve the importantfunction of continuously equalizing the pressure and density of thereference chamber 363, as explained in connection with the previouslydescribed embodiments. During its pressure-equalizing movements, thebellows 404) can expand up into the recessed mounting base 352 as far asthe limiting surface 355.

The bellows 4% is made of rubber or other suitable flexible material andis connected at its lower end to a vertical annular flange 464 of amounting ring 4G2 whose outer periphery rests on and is sealed to theupper surface of a shoulder 406 extending radially inwardly from theinner wall surface of the upper portion 338 of insulating housing 336.

When the combustion detection device 3H0 is secured to its uppermounting base 352 as shown in FIG. 5, the

external atmospheric pressure is communicated to the enclosed spacesurrounding bellows 4% by means of suitable passages 352 in mountingbase 352 which place the enclosed space surrounding the exterior surfaceof bellows 430 in communication with the external atmosphere.

-In order to eliminate any accumulation of moisture between the outersurface of the lower end of the bellows 4M and the inner surface ofinsulating housing 336, a weep hole 403 is provided through the wall ofinsulating housing 336 to drain condensate in this region to theexterior or" housing 336, from whence it may drain through passages 314and 316 in outer casing 302.

In order to equalize the pressure within the interior of bellows 4% withthe external atmospheric pressure when the combustion detection device300 is first placed in operation in a given location, screw valve 408 isprovided in the lower portion of insulating housing 336 below bellows4%, screw valve 408 being in screwthreaded engagement with a threadedpassage in the wall of housing 336. To equalize the internal pressure ofbellows 400 with that of the external atmosphere, screw valve 4% isremoved, permitting pressure equalization through the threaded passagewhich receives the screw valve. When the pressure has ben equalizedwithin the reference chamber, screw valve 408 is replaced in theposition shown in FIG. 5.

The operation of the combustion detection device 306 is substantiallythe same as that previously described for the embodiments of FIGS, 1-4.When combustion products are not present in the vicinity of the device300, the distribution of voltages across the series-connected test andreference chamber 335 and 368 is such that the potential of the controlgrid or trigger electrode 382 connected to common electrode 362 is notsufficiently positive to permit firing of gaseous tube 380. However, inthe presence of combustion products in test chamber 335, the impedanceto flow of ionization current in test chamber 335 increases to cause aredistribution of voltage across the test and reference chambers 335 and368, such that the potential of control grid or trigger electrode 382becomes sufiiciently positive to trigger the firing of gaseous dischargetube 380. The conduction through tube 360 causes energization of relaycoil 394 in the anode circuit of the tube to thereby close contact 396to energize a suitable alarm device. Conduction through tube 30 alsoprovides sufficient potential drop across resistance 392 in the outputcircuit of the tube to energize signal lamp 398.

It will be understood, of course, that the electrical circuitry shown inFIG. 7 for use with the modified embodiment of FIGS. 5 and 6 can be usedinterchangeably with any of the other illustrated embodiments of thecombustion detection device, and that similarly the electrical circuitryshown with the other embodiments can be used with the embodiment ofFIGS. 5 and 6.

The detection device of each of the embodiments of the inventiondescribed hereinbefore is so designed and proportioned that the testchamber which is open to the atmosphere operates in the non-saturatedrange of its current-voltage characteristic while the closed referencechamber works in the saturated region of its current-voltagecharacteristic.

It can be seen from the foregoing that there are provided in accordancewith the embodiments of the invention, a combustion gas or fire detectordevice of the ion ization type which is self-compensating for changes inthe density of the atmosphere being tested by the provision .of aflexible bellows or diaphragm which communicates external atmosphere.The equalization of the pressures of the test and reference chamberswith respect to each other prevents any false operation of the devicedue tomere changes in the density of the surrounding atmos phere andpermits the device to be used under conditions of extreme gas densityvariations. Furthermore, the use of a flexible diaphragm or bellowswhich maintains the interior of the reference chamber sealed from theexternal atmosphere and yet communicates any pressure changes in theexternal atmosphere due to changes in density of the surrounding gaseousmedium, prevents the entrance into the reference chamber of any moistureor foreign matter which would adversely affect the operation of thedevice. The flexible bellows and flexible diaphragm disclosed in theembodiments of the invention maintain the reference chamberherematically sealed at all times and yet permit equalization of the gaspressures and densities of the reference chamber and the test chamber. 7

There are also practical advantages to the several embodiments in whichmeans are combined with the combustion detection device for adjustingthe sensitivity of the detection device and for compensating forvariations in the triggering voltage of the gaseous discharge controltube. Also, the provision of the indicating lamp as part of thedetection device assembly, and which is energized when the gaseousdischarge tube becomes conductive,

rovides a convenient and efficient means directly at the location of thedetection device for indicating that the detection device has sensed thepresence of combustion products. This is of particular value where anumber of the detection devices are connected in parallel to a singlealarm device, since the use of the indicating lamp as part of thedetection device assembly permits a ready indication of which one of aplurality of detection devices has detected the presence of combustionproducts.

The embodiment shown in FIGS. 5, 6 and 7 has the further advantage thatthe gaseous discharge control tube is hermetically sealed in thereference chamber, thereby preventing condensation of moisture or othermatter on the tube which might adversely affect the operatingcharacteristics of the tube. Also, the embodiment of FIGS. 5, 6 and 7has the advantage that it includes a valve device to permit equalizationof the pressure interior of the reference chamber with that on theexterior of the reference chamber when the combustion detection deviceis first placed in operation in any given locality, to thereby permitthe internal pressure of the bellows to be conformed to the meanpressure at the particular locality where the combustion detectiondevice is installed. This adjustment is normally made only at the timeof the initial installation of the combustion detection device.

While there have been shown and described particular embodiments of theinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made therein without departing from theinvention and, therefore, it is aimed to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What I claim is:

1. Apparatus responsibe to changes in the composition of a gas,comprising a first ionization chamber readily accessible to the gas tobe tested and including a first electrode, a second ionization chamberincluding a second electrode, said second electrode including a firstportion thereof forming an end closure for said second chamber, saidsecond electrode also including a hollow cylindrical electrode portionupstanding from said first portion and extending into said secondchamber, a gaseous discharge control tube positioned in said hollowcylindrical electrode portion, said control tube including an anode, acathode and a control electrode, means connecting said control electrodeto said second electrode, said second electrode defining a commonelectrode intermediate said first and second chambers, a thirdelectrode, said third electrode being positioned in said second chambercoaxially of said hollow cylindrical electrode portion, means forionizing the gases in said chambers, flexible wall means positioned atone end of said second chamber and hermetically sealing said secondchamber, said flexible wall means communicating changes in pressure ofthe surrounding atmosphere to the hermetically sealed interior of saidsecond chamber whereby the density of the gas in said second chamber isequalized with that of the density of the surrounding atmosphere, andpower supply means connected across the anode and cathode of saidcontrol tube and across said first and third electrodes, said controltube being disposed to be energized by said control electrode uponchange in the composition of the gas being tested.

2. Apparatus as defined in claim 1 in which said flexible wall means isa bellows.

3. Apparatus responsive to changes in the composition of a gas,comprising an electrically conductive hollow casing, said casingincluding an apertured base portion and apertures in the wall of saidcasing adjacent said base portion to define a first ionization chamberreadily accessible to the gas to be tested, means supporting a source ofradioactive material in said first ionization chamber, an insulatinghousing positioned in said casing substantially coaxially of saidcasing, said insulating housing having a hollow interior open atopposite axial ends thereof and housing in the lower portion thereof asecond ionization chamber, a second electrode including a first portionthereof forming an end closure for the lower end of said insulatinghousing and second ionization chamber adjacent said base portion of saidcasing, said second electrode also including a hollow cylindricalelectrode portion upstanding from said first portion and extending intosaid insulating housing and into the second ionization chamber therein,said second electrode defining a common electrode for said first andsecond ionization chambers, a gaseous discharge control tube positionedin said hollow cylindrical electrode portion, said control tubeincluding an anode, a cathode and a control electrode, means connectingsaid control electrode to said common electrode of said first and secondionization chambers, a third electrode, said third electrode beingpositioned in said second ionization chamber coaxially of and radiallyoutwardly of said hollow cylindrical electrode portion, a source ofradioactive material in said second ionization chamber for ionizing thegas therein, flexible wall means closing the upper end of said secondionization chamber and hermetically sealing said second ionizationchamber, said flexible wall means communicating changes in pressure ofthe surrounding atmosphere to the hermetically sealed interior of saidsecond ionization chamber whereby the density of the gas in said secondionization chamber is equalized with that of the density of thesurrounding atmosphere, and power supply means connected across theanode and cathode of said control tube and across said electricallyconductive hollow casing and said third electrode, said control tubedisposed to be energized by said control electrode upon change in thecomposition of the gas being tested.

4. Apparatus as defined in claim 3 in which said flexible wall means isa bellows.

5. Apparatus responsive to changes in the composition of a gascomprising a test chamber open to the atmosphere of the gas beingtested, a first electrode being positioned in said test chamber, ahermetically-sealed gas-filled referen-ce chamber including a hollow"body member in axial alignment with said test chamber, said body memberbeing closed at an end thereof adjacent said test chamber by anelectrioally conductive closure member which forms a common electrode ofsaid test and reference chambers, flexible wall means closing theopposite end of said body member for communicating changes in pressureof the gas to be tested to the interior of said reference chamberwhereby the density of the gas in the reference chamber is equalizedwith that of the density of the surrounding atmosphere, a thirdelectrode positioned in said reference chamber intermediate the axiallength thereof and in l 1 o axially spaced relation to said commonelectrode, a source of electric power, said first and third electrodesconnected across said source of electric power to connect said test andreference chambers in electrical series, means for ionizing the gases insaid chambers and promoting current flow therethrough, and sensing meansresponsive to voltage variations connected across said first and thirdelectrodes and including a control electrode connected to said commonelectrode for rendering an indication of unbalanced current flow throughsaid chambers when a change occurs in the composition of the gas beingtested.

6. Apparatus responsive to changes in the composition of a gas as setforth in claim 5, in which said means for ionizing the gases in saidchamber is radioactive material, and axially displaceable means foradjustably shielding the radioactive material in said test chamber toselectively control the emission from said material.

7. Apparatus responsive to changes in the composition of a gas as setforth in claim 5, including support means connected within saidreference chamber, and said sensing means positioned within andsupported by said support means within aid reference chamber to shieldsaid sensing means from the means for ionizing the gas in said referencechamber and to prevent moisture condensation on said sensing means whenthe apparatus is subjected to varying atmospheric conditions.

8. Apparatus responsive to changes in the composition of a gas as setforth in claim 7, in which said support means comprises an extendedportion of said common electrode protruding interiorly of said referencechamber.

9. Apparatus responsive to changes in the composition of a gas as setforth in claim 5 in which said flexible wall means is a bellows.

10. Apparatus responsive to changes in the composition of a gas as setforth in claim 5, in which said third electrode is also disposed inconcentric spaced relation with said common electrode.

11. Apparatus responsive to changes in the composition of a gascomprising a test chamber open to the atmosphere of the gas beingtested, a first electrode positioned in said test chamber, ahermetically-sealed gas-filled reference chamber including a generallycylindrical body member formed of insulating material and in axialalignment with said test chamber, said body member being closed at anend thereof adjacent said test chamber by an electrically conductivedisk member which forms a common electrode of said test and referencechambers, said body member being closed at the opposite end thereof by aflexible wall means which communicates changes in pressure of the gas tobe tested to the interior of said reference chamber whereby the densityof the gas in the reference chamber is equalized with that of thedensity of the surrounding atmosphere, a third electrode positioned insaid reference chamber intermediate the axial length thereof and inaxially spaced relation to said common electrode, a source of electricpower, said first and third electrodes connected across said source ofelectric power to connect said test and reference chambers in electricalseries, means for ionizing the gases in said chambers to inhibit currentflow therethrough, and a gaseous discharge tube including an anode and acathode connected across said third and first electrodes, and a controlgrid for said tube connected to said common electrode or" said test andreference chambers for controlling the operation of said tube upon achange in the composition of the tested gas.

12. The apparatus defined in claim 11, including an indicating lightpositioned immediately adjacent said chambers and connected across saiddischarge tube, and relay means connected to respond to conduction ofsaid gaseous discharge tube and connected in the light circuit toenergize said indicating light upon a change in the composition of thetested gas. A

13. Apparatus responsive to changes in the composition of a gas as setforth in claim 11, and including potentiometer means connected betweensaid third electrode, first electrode and the cathode of said dischargetube, with the first electrode connected to the adjustable tap thereoffor varying the responsive sensitivity of the apparatus.

14. Apparatus responsive to changes in the composition of a gas,comprising a first ionization chamber provided with spaced electrodesand readily accessible to the gas to be tested, a second ionizationchamber pro vided with spaced electrodes, an electrode of each of saidchambers commonly connected to form a series junctionto connect saidchambers in electrical series, said second ionization chamber acting asa comparison chamber, said second chamber being hermetically-sealed andfilled with gas, said second chamber including a flexible wall portionwhich communicates changes in pressure of the gas to be tested to thehermetically-sealed interior of said second chamber where-by the densityof the ga in the second chamber is equalized with that of the density ofthe surrounding atmosphere, means for ionizing the gases in saidchambers, a control tube means responsive to voltage variations andincluding an anode and a cathode, and having a control electrodeconnected at the electrical junction between the series-connectedchambers, a source of direct current power, said anode connected withthe other electrode of said second ionization chamber and with saidsource of direct current power, said control electrode being adapted totrigger current conduction through said control tube means upon changein current fiow through said chambers, a resistance element, meansconnecting opposite ends of said resistance element across said sourceof direct current power, an adjustable tap movable to adjusted positionsalong said resistance element, means connecting the other electrodes ofsaid first and second ionization chambers between one end of saidresistance element and said adjustable tap, and means connecting saidcathode of said control tube means to the other end of said resistanceelement, whereby movement of said tap along said resistance element iseffective to vary the potential of said control electrode with respectto said cathode for varying the responsive sensitivity of the apparatus.

15. Apparatus responsive to changes in the composition of a gas,comprising a first ionization chamber provided with electrode means andreadily accessible to the gas to be tested, a second ionization chamberprovided with electrode means, said second ionization chamber acting asa comparison chamber, said second chamber being hermetically sealed andfilled with gas, said second chamber including a flexible wall portionin communication with the gas to be tested which communicates changes inpressure of the gas to the hermetically sealed interior of said secondchamber whereby the density of the gas in the second chamber isequalized with that of the density of the surrounding atmosphere, meansfor ionizing the gases in said chambers, a voltage source connectedacross selected electrode means of said ionization chambers, to connectsaid chambers in electrical series, and means sensitive to voltagevariations connected across the selected electrode means of saidchambers and across said voltage source and including control meansconnected with the remaining electrode means of the said chambers forcontrolling said means sensitive to voltage variations to render anindication when a change occurs in the composition of the gas beingtested.

16. Apparatus responsive to change in the composition of a gas as setforth in claim 15 with the addition of openable normally closed valvemeans connected to said second ionization chamber for initially settingthe internal pressure of said second ionization chamber with theexternal atmospheric pressure of the locale to initially position saidflexible wall portion in a substantially unstressed state.

17. Apparatus responsive to changes in the composi- 1 7 tion of a gas asset forth in claim 16 in which said openable normally closed valve meansis a screw.

18. Apparatus responsive to changes in the composition of a gas as setforth in claim 15 in which said electrode means in said first ionizationchamber and said electrode means in said second ionization chamber eachcomprises an individual pair of electrode members.

19. Apparatus responsive to changes in the composition of a gas as setforth in claim 15 in which the selected electrode means of theionization chambers comprise an electrode member disposed in said firstionization chamher and an electrode member disposed in said secondionization chamber, and the remaining electrode means comprises a singleelectrode member common to both of said chambers.

References Cited in the file of this patent UNITED STATES PATENTS1,332,341 Huffman et a1 Mar. 2, 1920 2,173,261 Marden Sept. 19, 19392,408,051 Donelian Sept. 24, 1946 2,659,390 MacLea et a1 Nov. 17, 19532,732,545 Pvassow et a1 Jan. 24, 1956 2,759,174 Brailstord Aug. 14, 1956

1. APPARATUS RESPONSIBLE TO CHANGES IN THE COMPOSITION OF A GAS,COMPRISING A FIRST IONIZATION CHAMBER READILY ACCESSIBLE TO THE GAS TOBE TESTED AND INCLUDING A FIRST ELECTRODE, A SECOND IONIZATION CHAMBERINCLUDING A SECOND ELECTRODE, SAID SECOND ELECTRODE INCLUDING A FIRSTPORTION THEREOF FORMING AN END CLOSURE FOR SAID SECOND CHAMBER, SAIDSECOND ELECTRODE ALSO INCLUDING A HOLLOW CYLINDRICAL ELECTRODE PORTIONUPSTANDING FROM SAID FIRST PORTION AND EXTENDING INTO SAID SECONDCHAMBER, A GASEOUS DISCHARGE CONTROL TUBE POSITIONED IN SAID HOLLOWCYLINDRICAL ELECTRODE PORTION, SAID CONTROL TUBE INCLUDING AN ANODE, ACATHODE AND A CONTROL ELECTRODE, MEANS CONNECTING SAID CONTROL ELECTRODETO SAID SECOND ELECTRODE, SAID SECOND ELECTRODE DEFINING A COMMONELECTRODE INTERMEDIATE SAID FIRST AND SECOND CHAMBERS, A THIRDELECTRODE, SAID THIRD ELECTRODE BEING POSITIONED IN SAID SECOND CHAMBERCOAXIALLY OF SAID HOLLOW CYLINDRICAL ELECTRODE PORTION, MEANS FORIONIZING THE GASES IN SAID CHAMBERS, FLEXIBLE WALL MEANS POSITIONED ATONE END OF SAID SECOND CHAMBER AND HERMETICALLY SEALING SAID SECONDCHAMBER, SAID FLEXIBLE WALL MEANS COMMUNICATING CHANGES IN PRESSURE OFTHE SURROUNDING ATMOSPHERE TO THE HERMETICALLY SEALED INTERIOR OF SAIDSECOND CHAMBER WHEREBY THE DENSITY OF THE GAS IN SAID SECOND CHAMBER ISEQUALIZED WITH THAT OF THE DENSITY OF THE SURROUNDING ATMOSPHERE, ANDPOWER SUPPLY MEANS CONNECTED ACROSS THE ANODE AND CATHODE OF SAIDCONTROL TUBE AND ACROSS SAID FIRST AND THIRD ELECTRODES, SAID CONTROLTUBE BEING DISPOSED TO BE ENERGIZED BY SAID CONTROL ELECTRODE UPONCHANGE IN THE COMPOSITION OF THE GAS BEING TESTED.